CCSBT-ESC/1409/35 1 Analysis for tuna catches of the Taiwanese southern bluefin tuna longline fishery Sheng-Ping Wang 1 , NorioTakahashi 2 and Tomoyuki Itoh 2 1 National Taiwan Ocean University, Taiwan 2 National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Japan 要約 台湾はえ縄データは有益なミナミマグロの資源指数を提供するものとして期待されてい る。資源指標のターゲッティングの問題を検討するため、台湾はえ縄漁業によるミナミマグ ロに関連する他のマグロ類の漁獲を記述した。ビンナガおよびメバチ、キハダ、メカジキの 漁獲は使用釣鈎数の単純な反映であった。ビンナガとメバチ、また TArea2 ではキハダも、 ターゲッティング問題でさらに検討すべき種であると示唆された。 Abstract Taiwanese longline data are expected to provide a useful abundance index of southern bluefin tuna. In order to examine the targeting issue for the index, we described catch of other tunas by Taiwanese longline fleet in relation to SBT. Catches of albacore, bigeye, yellowfin and swordfish were simple reflections of being proportional to the amount of hooks used. Results suggested that albacore and bigeye, and maybe yellowfin in TArea 2, are species to be further considered in targeting issues.
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Analysis for tuna catches of the Taiwanese southern bluefin tuna ...€¦ · of this fleet. TArea1 is 25.0S-39.9S and 60.0E -109.9E in the southeastern Indian Ocean. TArea2 is 20.0S-44.9S
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CCSBT-ESC/1409/35
1
Analysis for tuna catches of the Taiwanese southern bluefin tuna longline fishery
Sheng-Ping Wang1, NorioTakahashi2 and Tomoyuki Itoh2
1 National Taiwan Ocean University, Taiwan
2 National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Japan
要約 台湾はえ縄データは有益なミナミマグロの資源指数を提供するものとして期待されてい
る。資源指標のターゲッティングの問題を検討するため、台湾はえ縄漁業によるミナミマグ
ロに関連する他のマグロ類の漁獲を記述した。ビンナガおよびメバチ、キハダ、メカジキの
漁獲は使用釣鈎数の単純な反映であった。ビンナガとメバチ、また TArea2 ではキハダも、
ターゲッティング問題でさらに検討すべき種であると示唆された。 Abstract
Taiwanese longline data are expected to provide a useful abundance index of southern bluefin tuna. In order to examine the targeting issue for the index, we described catch of other tunas by Taiwanese longline fleet in relation to SBT. Catches of albacore, bigeye, yellowfin and swordfish were simple reflections of being proportional to the amount of hooks used. Results suggested that albacore and bigeye, and maybe yellowfin in TArea 2, are species to be further considered in targeting issues.
(SBT) in the 1980s. The fishery statistic data has been accumulated and thus it is expected to provide an abundance index useful for the stock assessment in the CCSBT. This index would be highly valuable as index for young fish of age 3-5.
Our aim is to develop an abundance index from Taiwanese longline data. Based on the CPUE standardization for Taiwanese SBT longline fishery and the description for the characteristics of Japanese SBT longline fishery (Itoh et al. 2013; Wang et al. 2013), we found several points: (1) Data collection of catch, effort and size for SBT was reformed and improved in 2002; (2) Taiwanese longline SBT fishing area in the southeast Indian Ocean is unique and has little overlap with Japanese longline SBT fishing ground; (3) SBT caught was mainly for age 3 or 4, sometimes age 5; (4) Little variation in age composition by longitude, latitude or month; (5) SBT was caught mainly between April and September.
We suggested using new statistical area for Taiwanese longline fleet (named as TArea) instead of the CCSBT statistical Areas based on consideration for the effort distribution of this fleet. TArea1 is 25.0S-39.9S and 60.0E-109.9E in the southeastern Indian Ocean. TArea2 is 20.0S-44.9S and 20.0E-59.9E in the southwestern Indian Ocean. Note that these boundaries are tentative and are subject to be modified by further examination.
It was suggested to consider the catch of other tunas, including bigeye tuna and yellowfin tuna, for the Taiwanese longline abundance index in the 2013 ESC. Such a suggestion was reasonable because SBT is not necessarily the target species in the Taiwanese longline fleet. Thus, in this document we will describe catch of other tunas in relation to SBT in the Taiwanese longline fleet.
2. Materials and methods
We used the dataset (Interim_CCSBT_DataCD_2014_Revised.mdb) in the CCSBT data exchange process where Secretariat compiled data files submitted from all Members. Datasets, including catch-and-effort and non_sbt_catches, were extracted. Taiwanese data were chosen by specifying COUNTRY_CODE as “TW”. 3. Results and discussion
The numbers of fish, as well as hooks used, by year are shown in Table 1 for top five fish species caught, southern bluefin tuna Thunnus maccoyii (SBT), albacore T. alalunga (ALB), bigeye tuna T. obesus (BET), yellowfin tuna T. albacares (YFT) and swordfish
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Xiphias gladius (SWO). It should be noted that the data analyses were divided into two time periods by year
of 2002 because Taiwanese SBT statistics system was reformed in 2002. The logbook was only source to produce the data report before 2001, and the SBT weekly report system was introduced in 2002 to the measurement monitoring and thus the reporting rate of SBT catch has substantially improved since then (Anon, 2014).
It also should be noted that SBT catch data become available immediately by the weekly report system, but catch data of other species do not become available unless logbooks were reported and its data were compiled. Therefore, catch data of other species in 2013 are incomplete and that in 2012 may be tentative.
Regardless of the change in SBT statistics system, albacore has been dominated as 92.7% in the total over 1981-2013 period. It was followed by bigeye (4.1%), yellowfin (1.5%), swordfish (1.0%) and SBT (0.7%). Species compositions were also calculated for TArea1 and TArea2, respectively (Table
2, Fig. 1, Fig. 2). Albacore also dominated the catch composition in both areas. SBT has been the second dominated species since 2004 in TArea1. In TArea2, SBT composition increased after 2005 and exceeded 10% in the following years. The Taiwanese data submitted to CCSBT covered largely in the southern hemisphere
of Indian Ocean. Distributions of effort and catch by month, latitude and longitude in all areas are shown in Fig. 3. Those in TArea 1 and TArea 2 are shown in Fig. 4 and Fig .5, respectively. Catches of albacore, bigeye, yellowfin and swordfish were simple reflections of being proportional to the amount of hooks used. This suggests that no particular operation pattern for targeting any one of the four species exists. Horizontal and vertical distributions or temperature preference were different by these species. If Taiwanese longline fleet had a specialized strategy for targeting one species in a
specific area and/or season, it would be happened that catch of this species was large but other species were not. If such an apparent pattern were observed, we should be careful very much for the targeting issue in CPUE standardization of SBT. If such a pattern was not observed, as in the present case, we could believe that SBT CPUE was not strongly affected by targeting issue. However, it does not deny the possibility of existence of targeting influence, and we need to consider how we check in the next step. Nominal CPUE, annual total catch / annual total hooks x 1000, in TArea1 and TArea2
are shown in Table 3 and Fig. 6. The largest CPUE has been of albacore. Because we will use data of from 2002 onward to develop SBT abundance index for Taiwanese fleet,
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CPUEs after 2002 are of our interest. In TArea 1, CPUE of SBT was the second highest in most of years. Bigeye CPUE was much lower, except 2002-2003 and 2010 and 2011 when SBT CPUE was low. CPUEs of yellowfin and swordfish were further lower than that of SBT. In TArea 2, the second highest CPUE was recorded by SBT, bigeye or yellowfin in this area. CPUE correlation between SBT and other tunas are shown in Fig. 7. No strong
correlation was observed between any two species. We have not reached a conclusion of how targeting affects SBT CPUE and how we
should deal with it. Our analysis suggests that albacore and bigeye, (and maybe yellowfin in TArea 2) are species to be further considered in targeting issues, and tables and figures in this document are useful to facilitate discussion for next step. 5. References Anon. (2014) Preparation of Taiwan’s Southern bluefin tuna catch and effort data
submission for 2014. CCSBT-ESC/1409/45. Itoh, T. S. P. Wang, and N. Takahashi (2013) Progress in analysis of historical fishery
data for Taiwanese southern bluefin tuna fleet. CCSBT-ESC/1309/38. Wang, S. P., S. T. Chang and S. L. Lin (2013) CPUE analysis for southern bluefin tuna
caught by Taiwanese longline fleet. CCSBT-ESC/1309/37
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Table 1. Total numbers by year for five species and hooks by Taiwanese longline.
SBT CPUE after 2002 will be used for abundance index.
Fig 1. Species composition of five species for Taiwanese longline in TArea 1.
Years between 2001 and 2002 were marked because SBT CPUE after 2002 will be used for abundance
index.
Fig 2. Species composition of five species for Taiwanese longline in TArea 2.
Years between 2001 and 2002 were marked because SBT CPUE after 2002 will be used for abundance
index.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
2013
Catch compo
sition
Year
SWO
YFT
BET
ALB
SBT
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
2013
Catch compo
siton
Year
SWO
YFT
BET
ALB
SBT
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Fig 3. Distribution of numbers of hooks or species caught by month, latitude or longitude to
year in Taiwanese longline for all area. (by Month)
Years between 2001 and 2002 were marked because SBT CPUE after 2002 will be used for abundance index.
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Fig 3. (cont’d) (by latitude)
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Fig 3. (cont’d) (by longitude)
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Fig 4. Distribution of numbers of hooks or species caught by month, latitude or longitude to
year in Taiwanese longline in TArea 1. (by Month)
Years between 2001 and 2002 were marked because SBT CPUE after 2002 will be used for abundance index.
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Fig 4. (cont’d) (by latitude)
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Fig 4. (cont’d) (by longitude)
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Fig 5. Distribution of numbers of hooks or species caught by month, latitude or longitude to
year in Taiwanese longline in TArea 2. (by Month)
Years between 2001 and 2002 were marked because SBT CPUE after 2002 will be used for abundance index.
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Fig 5. (cont’d) (by latitude)
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Fig 5. (cont’d) (by longitude)
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TArea 1 TArea 2
Fig 6. Nominal CPUE by year, area and species for Taiwanese longline.
Top panels are of five species for the period since 1981. Middle panels are of four species excluding albacore for the period since 1981. Bottom panels are of four species for the short period since 2002 corresponding to years for which SBT CPUE data will be used for abundance index. 2013 data were removed because logbook data of this year was tentative. Left and right panels are for TArea1 and TArea2, respectively.
0.0
5.0
10.0
15.0
20.0
25.0
1980 1990 2000 2010
Nom
inal CPU
E
Year
SBT
ALB
BET
YFT
SWO
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1980 1990 2000 2010
Nom
inal CPU
E
Year
SBT
BET
YFT
SWO
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
1980 1990 2000 2010
Nom
inal CPU
E
Year
SBT
ALB
BET
YFT
SWO
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
1980 1990 2000 2010
Nom
inal CPU
E
Year
SBT
BET
YFT
SWO
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
2002 2004 2006 2008 2010 2012
Nom
inal CPU
E
Year
SBT
ALB
BET
YFT
SWO
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
2002 2004 2006 2008 2010 2012
Nom
inal CPU
E
Year
SBT
ALB
BET
YFT
SWO
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Fig 7. Plot of CPUE to SBT in TArea 1 in Taiwanese longline.
“r” is the Pearson`s correlation factor. Year in data are between 2002 and 2012.